Design And Construction Of A Microcontroller Based Single Phase Automatic Changeover Switch

ABSTRACT

Power instability or outage in general does not promote development in the public and private sector. The investors do not feel secure to come into a country with constant or frequent power failure. These limit the development of industries. In addition, there are processes that cannot be interrupted because of their importance for instance, surgery operation in hospitals, transfer of money between banks and lots more. Power instability and outage in developing countries (Nigeria) creates a need for alternative sources of power to back up the mains supply.

This research covers the design and construction of a single phase microcontroller-based automatic power changeover. It has the capacity to automatically switch power from national grid to generator and vice versa, once there is power failure in any of the two power supplies. This was achieved by the use of electrical components such as resistors, capacitors, diodes, transistors, opto-isolators etc., integrated circuits that have timing abilities and relays for switching effect. Due to the looping of the pole of the contactor to give 50A current each for PHCN and generator, the maximum power the circuit can withstand on an a.c voltage of 240V is 12KVA. This means the circuit can carry a large amount of power in homes and offices.

TABLE OF CONTENTS

 TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWLEDGEMENT

ABSTRACT

TABLE OF CONTENT

CHAPTER ONE

• INTRODUCTION
• BACKGROUND OF THE PROJECT
• PROBLEM STATEMENT
• AIM/OBJECTIVE OF THE PROJECT
• SIGNIFICANCE OF THE PROJECT
• PURPOSE OF THE PROJECT
• SCOPE OF THE PROJECT
• APPLICATION OF THE PROJECT
• DEFINITION OF TERMS
• PROJECT ORGANISATION

CHAPTER TWO

2.0      LITERATURE REVIEW

2.1      OVERVIEW OF RELEVANT TECHNOLOGY

2.2      REVIEW OF EXISTING SYSTEM

2.3      REVIEW OF RELATED PROJECT

2.4       REVIEW OF FUNDAMENTAL CONCEPTS

2.5      REVIEW OF COMPONENTS USED

2.6      SUMMARY OF REVIEWED WORKS

CHAPTER THREE

3.0      METHODOLOGY

3.1      BLOCK DIAGRAM

3.2      CIRCUIT DIAGRAM

3.3      CIRCUIT DIAGRAM

3.4      SYSTEM FLOWCHART

3.5      CIRCUIT ANALYSIS AND CALCULATIONS

3.6      PROGRAM CODE

CHAPTER FOUR

4.0       RESULT ANALYSIS

4.1      CONSTRUCTION PROCEDURE AND TESTING

4.2      ASSEMBLING OF SECTIONS

4.3      RESULT

4.4     DISCUSSION

CHAPTER FIVE

• CONCLUSIONS
• RECOMMENDATION

REFERENCES

CHAPTER ONE

1.0                                                        INTRODUCTION

• BACKGROUND OF THE PROJECT

If some of these big firm do not make provisions for stand-by power source, frustration could set in which may lead to the closure of business and thus throwing workers into unemployment. Also in the case of hospital, undergoing a surgical operation and power supply suddenly go off, the patient might lose his or her life due to the power outage (Horowitz, 2015).

An Engineering Author, “Tony Rudkin” said in his book titled “Upgraded Signal Source with Improved Performance and Reliability” that the cost and depredation associated with breakdown vary from one application to the other, and in some cases, the user has little choice but to ensure that a stand-by unit is available to take over on event of failure of primary system (Tony, 2015).

Furthermore, if the president of the country is making nationwide broadcast and all of a sudden power went off in the transmitting station, it would be viewed as an attempt to sabotage the government ruling and some people must pay for it according to Horowitz (2015).

Sequel to the rate at which more sophisticated electrical gadgets are being procured and installed in our homes, hospitals and business premises, there is a justifiable need for a faster and more reliable change over system in an event of power outage.

The research project is designed for power supply applications. It involves automatic change over between the mains power supply and a standby generating set. The project implements an automatic switching or starting of the power generator, whenever the main power fails. The circuit of the project consists of logical control units, display units, alarm units and relay switches. The design of the project takes into consideration practical or real life situations and a lot of precautions were put in place to make its performance acceptable, even though it is a prototype design. The basic operation of the project is to switch ON an auxiliary power supply (a generator). This operation connects the power supply from the generator to the load after a predetermined time interval. This is intended to normalize the current from the generator. Switching is possible through the use of the relays. The system was designed to automatically change power supply back to the main supply moments, after the A.C. mains are restored and to switch OFF the generator.

This project, however is designed and implemented as a micro-processor based controlled system, specifically using the micro-controller as its basic component. It is a dedicated embedded system.

1.2                                                  PROBLEM STATEMENT

Power failure or outage in developing countries such as Nigeria is highly detrimental. The insecurity associated with constant or frequent power failure or outage brings about limitation to power consistent investments, thus hampering the development of industries and multinational ventures (Ahmed et al., 2006). Processes like carrying out surgical operations in hospitals, laboratories which require constant power supply for research, money transactions between banks and more require constant use of uninterrupted power. In other to solve this problem, an automatic changeover switch was invented. This research covers the design and construction of a single phase digital automatic power changeover. It has the capacity to automatically switch power from  national grid to generator and vice versa, once there is power failure in any of the two power supplies and at the same time has the capacity of shutting down a generator set once the mains grid is been restored.

1.3                                 AIMS AND OBJECTIVES OF THE PROJECT

The main aim of this work is to build an automatic changeover switch for single phase power supply using microcontroller. The objectives are:

1. To setup a switching device that will change to an alternative power supply (Generator), and back to the main supply when it is restored.
2. To provide uninterrupted power supply at all times

• To provide alternative source of power supply

1. To automatically trip OFF and ON a generator set when mains power supply is fails and restored.

1.4                              SCOPE AND LIMITATION OF THE STUDY

This scope of this work covers only building a single phase automatic changeover which can only be used for providing a means of switching from one phase of AC mains to generator in the case of failure in public utility.

Microcontrollers are the heart of embedded systems. There are various types of embedded systems for different applications. The applications of embedded systems range from controlling appliances. When it comes to controlling high voltage devices, microcontrollers often depend on Relays to drive them. Relays act as a bridge between the low power microcontrollers and high voltage devices.

The system has a generator trip OFF mechanism which turns ON and OFF the generator, in accordance to the program run in Read Only Memory (ROM) of the microcontroller.

Finally, the system have an alarm circuit which sounds on four conditions:

1. When power fails
2. When power is restored

• If a command is given for generator to start and it refuses after the six trials

1. If a command is given for generator to stop and it refuses

1.5                                         SIGNIFICANCE OF THE PROJECT

The automatic change over switch has the following advantages;

1. It minimizes damages to lives/equipment since it has its own monitoring system and its switching requires no human contact with the switch, thus eliminating human error.
2. It reduces its change over timing to the minimum due to its fast response to power outage.
3. It maintains high quality of service through its fast and prompt response.

Moreover, the size and captivity of the unit will depend upon the load for which it will be used. The unit is also portable, easy, convenient and safe to install.

1.6                                              PURPOSE OF THE PROJECT

The purpose of this project is to maintain constant supply to the main circuit that is being supplied by making-up for the time lapse or delay that usually accompanies the manual switching from one source to another. The design comprises of the power connection circuit and control connection circuit. The main components to be used include; relays, microcontroller, and transistor

1.7                                          APPLICATION OF THE PROJECT

Some common examples of entities that implement automatic switches out of necessity are: hospitals, data centers, jails and prisons, fire departments, defense organizations, and police departments.

1.8                                                  DEFINITION OF TERMS

CHANGEOVER: Generally, a changeover switch is a system which could be operated manually or automatically , that changes one source of power supply to another source in case of power failure from either of the two sources.

RELAY: relay is one of the major components used in this work which is an electrical device, typically incorporating an electromagnet, which is activated by a current or signal in one circuit to open or close another circuit.

POWER FAILURE: is a short- or long-term loss of the electric power to an area.       

1.9                                                         PROJECT ORGANISATION

The work is organized as follows: chapter one discuses the introductory part of the work,   chapter two presents the literature review of the study,  chapter three describes the methods applied, chapter four discusses the results of the work, chapter five summarizes the research outcomes and the recommendations.